Complement activation occurs primarily by three pathways: the so-called classical pathway, the lectin pathway and the alternative pathway. The key proteins involved in the activation of the alternative pathway are factor B (fB) and factor D (fD). These proteins work in concert to initiate and/or to amplify the activation of C3, which then leads to the initiation of a number of inflammatory events. A third protein, properdin, stabilizes the complex of C3 and factor B but is not absolutely required for the alternative pathway to function. Factor B also helps solubilize immune complexes, has been reported to act as a B cell growth factor and can activate monocytes (Takahashi, 1980; Hall, 1982; Peters, 1988). Factor B-deficient mice (fB−/− mice) have been generated and IgG1 antibody response to T-cell dependent antigens and sensitivity to endotoxic shock appear normal in these mice (Matsumoto, 1997).
The alternative complement pathway is usually initiated by bacteria, parasites, viruses or fungi, although IgA Abs and certain Ig L chains have also been reported to activate this pathway. Alternative pathway activation is initiated when circulating factor B binds to activated C3 (either C3b or C3H2O). This complex is then cleaved by circulating factor D to yield an enzymatically active fragment, C3bBb. C3bBb cleaves C3 generating C3b, which drives inflammation and also further amplifies the activation process, generating a positive feedback loop. Both components (factor B and factor D) are required to enable activation of the alternative pathway.
Recent studies have shown that the alternative pathway of complement plays an important role in the pathogenesis of several animal models of disease. For example, complement activation within the kidney after ischemia reperfusion injury (I/R) is mediated almost exclusively by the alternative pathway (Thurman et al., 2003, J Immunol 170:1517-1523), and the alternative pathway plays a critical role in the development of inflammatory arthritis. Perhaps most surprisingly, mice deficient in the alternative pathway have been demonstrated to be protected from nephritis in the MRL/lpr model of lupus nephritis (Watanabe et al., 2000, J Immunol 164:786-794) and from anti-phospholipid mediated fetal loss (Girardi et al., 2003, J Clin Invest 112:1644-1654), models that would traditionally have been assumed to be mediated by the classical complement pathway. In addition, Nataf et al. has shown that, in an experimental autoimmune encephalomyelitis (EAE) model, in both C3(−/−) and factor B(−/−) mice, there was little infiltration of the parenchyma by macrophages and T cells and, as compared with their wild-type littermates, the central nervous systems (CNS) of both C3(−/−) and factor B(−/−) mice induced for EAE are protected from demyelination (Nataf et al., 2000, J. Immunol. 165:5867-5873). Subsequent studies of autoimmune pathology in C4 (−/−) mice in the EAE model showed that deletion of the C4 gene does not significantly change either the time of onset or the severity and tempo of myelin oligodendrocyte-induced EAE compared with controls with a fully intact complement system, indicating that the contribution of murine complement to the pathogenesis of demyelinating disease is realized via the alternative pathway (Boos et al., 2005, Glia 49:158-160).
Traumatic brain injury (also referred to herein as TBI) is a condition with very deleterious effects on an individual's health that currently has no effective treatment. Complement activation has been shown to be involved in the development of brain damage following TBI (Bellander et al., 2001, J. Neurotrauma 18:1295-1311; Kaczorowski et al., 1995, J. Cereb. Blood Flow Metab. 15:860-864; Keeling et al., 2000, J. Neuroimmunol. 105:20-30; Schmidt et al., 2004, Eur. J. Trauma 30:135-149; Nataf et al., 1999, Trends Neurosci 22:397-402; Stahel et al., 1998, Brain Res. Rev. 27:243-256; Stahel et al., 2001, J. Neurotrauma 18:773-781; Van Beek et al., 2003, Ann NY Acad Sci 992:56-71; Rancan et al., 2003, J. Cereb. Blood Flow & Metab. 23:1070-1074). However, these studies have focused on the effects of the complement cascade at a point where all three pathways that activate complement converge, such as at C3 (see, for example, Rancan et al., 2003, ibid.). Therefore, prior to the present invention, there have been no reports showing whether one of the complement pathways is preferentially or exclusively activated as a result of TBI, or is required to develop TBI.
The immediate goal in the management of head-injured patients is the prevention of secondary brain damage by rapid correction of hypotension, hypoxemia, hypercarbia and hypoglycemia. The main priority in the early management of head trauma patients is the maintenance of an adequate cerebral perfusion pressure (CPP), which should be above 70-80 mmHg. Different therapeutic approaches are aimed at lowering the intracranial pressure (ICP) in order to keep an adequate CPP. Among the therapeutic modalities are: the reduction of mass lesions by surgical evacuation of intracranial hematomas, the reduction of brain swelling with osmotic drugs (e.g., mannitol), and the therapeutic drainage of cerebrospinal fluid (CSF) through intraventricular catheters. Patients with severe TBI are transferred to intensive care unit (ICU) at the earliest timepoint and treated according to standardized protocols. Goals of ICU therapy include: achievement and maintenance of adequate gas exchange and circulatory stability, prevention of hypoxemia and hypercarbia, repeated, scheduled computerized tomography (CT) scans for detection of delayed secondary intracranial pathology, profound sedation and analgesia to avoid stress and pain, achievement and maintenance of optimal CPP (>70 mmHg) and cerebral oxygen balance, avoidance of hyperthermia (<38° C.), prevention of hyperglycemia and hyponatremia, no routinely performed head elevation, prevention of stress ulcers and maintenance of gut mucosal integrity, and prophylaxis for complicating factors (e.g. pneumonia or meningitis). In the event of elevated ICP (>15 mmHg, >5 minutes), patients can be treated by (1) deepening of sedation, analgesia, muscle relaxation; (2) CSF drainage through ventricular catheters; (3) moderate hyperventilation (under certain circumstances); (4) osmotherapy; (5) moderate hypothermia (±34° C.); and (6) barbiturate coma.
Spinal Cord Injury (also referred to herein as SCI) is also a condition of the central nervous system with very deleterious effects on an individual's health that currently has no effective treatment. Complement activation has been shown to be involved in the development of damage following SCI (Anderson et al., 2004, J Neurotrauma 21 (12):1831-46; Reynolds et al., 2004, Ann NY Acad Sci. 1035:165-78; Rebhun et al., 1991, Ann Allergy 66 (4):335-8). However, as with TBI, these studies have focused on the effects of the complement cascade at a point where all three pathways that activate complement converge, or have suggested a role for all complement pathways subsequent to SCI. Therefore, prior to the present invention, there have been no reports showing whether one of the complement pathways is preferentially or exclusively activated as a result of SCI, or is required to develop SCI.
SCI is generally defined as damage to the spinal cord that results in a loss of function, such as mobility or feeling. Frequent causes of damage are trauma (e.g., by car accident, gunshot, falls, etc.) or disease (polio, spina bifida, Friedreich's Ataxia, etc.). The spinal cord does not have to be severed in order for a loss of functioning to occur. In fact, in most individuals with SCI, the spinal cord is intact, but the damage to it results in loss of function. Besides a loss of sensation or motor function, individuals with SCI may also experience dysfunction of the bowel and bladder, sexual and fertility dysfunction, inability to regulate blood pressure effectively, reduced control of body temperature, inability to sweat below the level of injury, and chronic pain. Very high injuries (C-1, C-2) can result in a loss of many involuntary functions including the ability to breathe, necessitating breathing aids such as mechanical ventilators or diaphragmatic pacemakers.
Currently there is no cure for SCI. The immediate goal in the management of SCI patients is focused on decreasing damage as soon as possible after the injury occurs. Steroid drugs such as methylprednisolone reduce swelling, which is a common cause of secondary damage at the time of injury. There are several types of treatment in the short term for a spinal cord injury. First, the spine in the area of the injured spinal cord is immobilized to prevent further injury to the cord (e.g., using halos, casts, braces and straps). To reduce swelling in the spinal cord caused by injury, steroid medication is usually given during the first 24 hours following injury, although the more typical approach is to give steroid medication to those patients with neurological deficits and a time window of initiation of therapy within less than 8 hours after trauma (Bracken, 2001, Spine 26 (24S):S47-S54). Other medical treatment is often necessary, depending on complications that may develop. Because traumatic injury to the spinal cord usually involves an injury to the bones and ligaments of the spine, surgery may be performed. The aim of some surgeries is to remove bone (decompression) that is pressing on or into the spinal cord, or to stabilize or realign the spine in the area of the spinal cord injury when the vertebrae or ligaments have been damaged. Metal rods or cages and screws may be attached to normal vertebrae to prevent movement of fractured vertebrae and the vertebrae may be “fused” together using bone graft or the same reason. Stretching of the spine using weights and pulleys (called traction) may also help with alignment of the spine.
Despite the protocols for treatment of patients with TBI, potential complications from TBI therapy can include: cerebral vasospasms or cardiovascular depression, hepatotoxicity, immunosuppression, and increased incidence of pulmonary infections. In addition, although treatments for SCI may provide modest reductions in physiological damage, many protocols are primarily useful to help reduce the likelihood of further damage and to stabilize the patient. No single protocol has been proven to be entirely satisfactory for inhibiting the development of the physiological damage resulting from TBI or SCI. Therefore, there is a continuing need in the art for therapeutic processes and reagents having less toxicity and more specificity for the underlying cause of damage resulting from TBI and SCI.